Abstract
PurposeTo determine the measurement reliability of CorVis ST, a dynamic Scheimpflug analyser, in virgin and post-photorefractive keratectomy (PRK) eyes and compare the results between these two groups.MethodsForty virgin eyes and 42 post-PRK eyes underwent CorVis ST measurements performed by two technicians. Repeatability was evaluated by comparing three consecutive measurements by technician A. Reproducibility was determined by comparing the first measurement by technician A with one performed by technician B. Intraobserver and interobserver intraclass correlation coefficients (ICCs) were calculated. Univariate analysis of covariance (ANCOVA) was used to compare measured parameters between virgin and post-PRK eyes.ResultsThe intraocular pressure (IOP), central corneal thickness (CCT) and 1st applanation time demonstrated good intraobserver repeatability and interobserver reproducibility (ICC≧0.90) in virgin and post-PRK eyes. The deformation amplitude showed a good or close to good repeatability and reproducibility in both groups (ICC≧0.88). The CCT correlated positively with 1st applanation time (r = 0.437 and 0.483, respectively, p<0.05) and negatively with deformation amplitude (r = −0.384 and −0.375, respectively, p<0.05) in both groups. Compared to post-PRK eyes, virgin eyes showed longer 1st applanation time (7.29±0.21 vs. 6.96±0.17 ms, p<0.05) and lower deformation amplitude (1.06±0.07 vs. 1.17±0.08 mm, p<0.05).ConclusionsCorVis ST demonstrated reliable measurements for CCT, IOP, and 1st applanation time, as well as relatively reliable measurement for deformation amplitude in both virgin and post-PRK eyes. There were differences in 1st applanation time and deformation amplitude between virgin and post-PRK eyes, which may reflect corneal biomechanical changes occurring after the surgery in the latter.
Highlights
The cornea is a viscoelastic structure with quantifiable biomechanical properties [1]. These properties are related to corneal thickness, age, intraocular pressure (IOP), hydration, and various pathologies [2,3,4,5]
In the virgin-eye group, the values of central corneal thickness (CCT) measured by Precisio, IOP measured by Icare rebound tonometer, and mean simK measured by OPD Scan II were not significantly different from the preoperative values of the post-postphotorefractive keratectomy (PRK) group (Table 1)
Similar to the studies performed by Nemeth et al [16] and Hon et al [15], we found that the following parameters had the best repeatability in both groups: CCT, IOP, 1st applanation time, and deformation amplitude
Summary
The cornea is a viscoelastic structure with quantifiable biomechanical properties [1]. These properties are related to corneal thickness, age, intraocular pressure (IOP), hydration, and various pathologies [2,3,4,5]. The ability to quantify corneal biomechanical failure represents an important step towards better understanding and treatment of keratectatic diseases. Corneal refractive laser ablation in virgin eyes weakens the cornea mechanically due to tissue removal, leading to deterioration in corneal biomechanical strength [8]. Knowledge of corneal biomechanical properties is important in predicting clinical outcomes [11] and in identifying cases with high risk for postoperative keratectasia after corneal refractive surgery
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